The continued growth of wireless communications has led to traditional cellular networks facilitating data and voice communications with various types of mobile terminals, such as mobile telephones, personal digital assistants, and personal computers configured with appropriate wireless modems. Recently, wireless local area networks (WLANs) have come to fruition, and are expanding at a rapid rate. Typically, personal computers and like computing devices are equipped with wireless modems to facilitate wireless communications between the computing device and one or more Access Points, which facilitate wireless communications with the computing device and a traditional local area network.
In addition to the introduction of WLAN standards (IEEE 802.1a/b/g), cellular standards (CDMA, UMTS) are evolving to facilitate data communication; however, none of these standards are compatible at a radio interface level with those used for WLANs. At the same time, users increasingly need an “always on” data communication ability regardless of their location. Cellular wireless networks and WLANs complement each other, in terms of where they provide coverage: cellular wireless networks are ubiquitous, whereas WLANs currently only provide spot coverage—albeit often in places where the cellular wireless radio signal has difficulty penetrating, such as inside buildings and in underground public transport stations. As users move from a coverage area of one radio technology into a coverage area of another radio technology, radio coverage of the two technologies could in some cases overlap, and in others not. Where radio coverage does not overlap, there is a clear benefit to being able to switch from one radio technology to the other when the coverage or radio signal changes. Even in the cases where the radio coverage overlaps, by switching radio technology, users could benefit from the higher throughput offered currently by any one of the WLAN radio technologies compared to any one of the cellular radio technologies. In this kind of an integrated, dual-radio and in general, multi-radio environment, there is a need to provide an efficient and uninterrupted transition from being serviced by one radio technology to being serviced by another radio technology. Such a transition is referred to as an inter-technology handoff.
Accordingly, there is a need for a technique to facilitate handoffs between cellular networks and WLANs in an efficient and effective manner. Further, there is a need to minimize the impact of handoffs on existing network infrastructures to minimize the implementation cost for a system capable of providing such handoffs. Finally, there is a need to minimize the impact of the handoff mechanism on the existing cellular and WLAN standards.